Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plant roots and cause annual agricultural losses of nearly ten billion dollars in the United States. One problem with controlling nematodes chemically is that the few chemicals available for this purpose are far from perfect with respect to environmental safety, mammalian toxicity, or expense. Because many plants are resistant to nematode attack because they contain nematode-toxic chemicals in their tissues, plants themselves can provide a potential source of new compounds useful for controlling nematodes. Therefore, this review article examines the wide variety of plant components discovered to possess nematode-antagonistic activity. The review is organized according to the chemical structures of the dozens of compounds identified thus far; their relative activities against nematodes are presented for comparative purposes. Unfortunately, not many plant families have been examined for naturally occurring nematicidal compounds. In addition to possible use as control tools, these chemicals can be used as starting materials that synthetic chemists can modify to yield other compounds with enhanced activity. This is a significant review article because the subject matter area has not been reviewed in a decade. The information contained in this review will be used by scientists developing safe and selective methods for controlling plant-parasitic nematodes.

Technical Abstract:
This review examines the discovery of naturally occurring phytochemicals antagonistic towards plant-parasitic and other nematodes. Higher plants have yielded a broad spectrum of active compounds, including polythienyls, isothiocyanates, glucosinolates, cyanogenic glycosides, polyacetylenes, alkaloids, lipids, terpenoids, sesquiterpenoids, diterpenoids, quassinoids, steroids, triterpenoids, simple and complex phenolics, and several other classes. Many other antinematodal compounds have been isolated from biocontrol and other fungi. Natural products active against mammalian parasites can serve as useful sources of compounds for examination of activity against plant parasites. The agricultural utilization of phytochemicals is currently limited by economics in many situations but offers tremendous potential.